The rotary machine used for an industrial compressor, a turbo refrigerator, a small gas turbine and the like, comprises an impeller provided with a plurality of blades on a disk fixed to a rotation shaft of the rotor. The rotary machine provides pressure energy and velocity energy to a gas by rotating the impeller.
As the above-described impeller, a so-called closed-impeller in which a cover is integrally fixed to blades is known. In a case where this closed-impeller is produced as a single-piece product, like, for example, Japanese Unexamined Patent Application, First Publication No. 2009-156122, complex cutting and welding are required, and it takes time for an assembling work of the impeller.
In addition, Japanese Unexamined Patent Application, First Publication No. 2003-293988 shows a producing method of an impeller performing a diffusion bonding in such a way that flow passages between the blades, the flow passages being formed by an inner circumferential side part and an outer circumferential side part, are connected to each other. The impeller of Japanese Unexamined Patent Application, First Publication No. 2003-293988 has a value in access for machining tools in both the inner circumferential side part and the outer circumferential side part, but the flow passages are required to be formed in both of the inner circumferential side part and the outer circumferential side part, and the diffusion bonding is required to performed so as to communicate the flow passages with each other. Thus, this leads to an increase in production costs.
On the other hand, an impeller assembled on the rotation shaft by performing shrink fitting of an inner diameter portion formed on a base portion side of the disk is known. In a case of applying this impeller, since the disk portion having a relatively large thermal capacity is disposed in the vicinity of the inner diameter portion, the temperature of the inner diameter portion does not rise easily when the impeller is disassembled from the rotation axis by heating the inner diameter portion.
Therefore, for example as shown in FIG. 10, a portion extending in one side in a direction of an axis O (left side in FIG. 10) is formed at an inner diameter portion 420, and the inner diameter portion 420 is performed shrink fitting to be fitted on the rotation shaft at a position being spaced apart from disk portion 430 (the position of shrink fitting is shown by the thick line in FIG. 10). This allows achieving easily assembling and disassembling of the impeller to and from the rotation axis, because the shrink fitting can perform at the portion having a small thermal capacity.
However, since the inner diameter portion 420 is disposed below a blade portion 440 and a cover 450, the space below the blade portion 440 and the cover 450 becomes small, and, in particular, when the welding between the blade portion 440 and the disk portion 430 in the side of rotation shaft 5 and the welding between the blade portion 440 and the cover 450, a space S for using the tools cannot secure sufficiently. Thus, there is a possibility that variations occur on the quality of the finished product.
In addition, the materials forming the disk portion 430, the blade portion 440 and the cover portion 450, are limited to use materials having a good in welding property, because the disk portion 430, the blade portion 440 and the cover portion 450 is required to be joined by welding, or the like. Therefore, the degree of freedom in design is limited.
In contrast, to secure the space S and improve the degree of freedom in design, the structure for example as shown in FIG. 11 can be considered. The impeller 410 shown in FIG. 11 divides the disk portion 430 and the inner diameter portion 420 with a surface m along the axis O of the rotation shaft 5, and is formed in a single-piece by the disk portion 430, the blade portion 440 and the cover portion 450. Then, the base portion of the disk portion 430 is mounted on the inner diameter portion 420 by shrink fitting. Accordingly, the disk portion 430, the blade portion 440 and the cover portion 450 do not necessarily need to be joined by welding, but when being joined by welding, the space for welding can be sufficiently secured.